4- Pressure :
Everything behaves differently under pressure, especially chemical reactions (like the process of making coffee). As pressure increases, the force exerted on dissolved substances leads to a faster extraction process, which can remove some substances that remain unchanged in the absence of pressure.
Placing a gas under pressure makes it soluble in liquids, resulting in more gas in a compressed liquid. Depressurization has the opposite effect, causing the gas to escape from the liquid; a prime example is opening a can of Coca-Cola.
The most popular method of preparing coffee using pressure is espresso. Espresso machines produce pressure equivalent to approximately nine times the pressure at sea level. Many solvents are released due to this pressure, and the water reacts with numerous gases, resulting in what we call crema.
